How to rotate the arms on the x axis on a lot of keyframes
If you go to the Graph Editor with the relevant bone selected in the 3D view, you can select and manipulate the handles controlling the keyframes for the particular value you want.  So for the left forearm, I think the value you may want to control is "W Quaternion Rotation".  Type A once or twice to make sure nothing is selected, then select one of the control point handles for WQuaternionRotation, then type L (select linked).  Then type G to move the values up or down for all of the keyframes.